Solar Panel Tracking and Mounting System

ABSTRACT

A method for tracking solar panels includes the steps (a) beginning a tracking cycle substantially at sunrise with adjacent tilting panels all horizontal, (b) tilting the adjacent panels in unison in a first angular direction toward the rising sun at a tilt rate that just avoids shading of adjacent panels, (c) reversing direction of panel tilt at a point that the panels reach either a maximum tilt limited by mechanical design, or the panel surfaces are orthogonal to the rising sun, (d) tilting the adjacent panels in a second angular direction, following movement of the sun and keeping the surface of the panels at right angles to the sun&#39;s position, until a point is reached that shadowing is imminent from the angle of the setting sun, and (e) reversing direction of panel tilt again to the first angular direction, adjusting tilt as the sun sets to avoid shading until the panels are again horizontal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority to a U.S. provisional patentapplication Ser. Nos. 61/217,794, filed on Jun. 3, 2009, 61/268,237,filed on Jun. 9, 2009, and 61/311,745, filed on Mar. 8, 2010,disclosures of which are incorporated at least by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of solar tracking systems andpertains particularly to methods and apparatus for tracking the sunusing at least one tilt angle while minimizing any shadowing on adjacentsolar collection panels.

2. Discussion of the State of the Art

In the field of solar tracking systems, there are system that canproduce substantially more energy (watts/panel) compared to fixed arraysof the same type and capacity by enabling tracking of the sun. Thisdifference is most pronounced for those using crystalline silicon PVtechnologies, where a single-axis tracking systems could add up to 30%more energy. However, there is a drawback involved. When one side ofarray is raised at low sun angles, the arrays cast larger shadows andrequire greater separation compared to their fixed counterparts. Again,this penalty is costliest for crystalline PV systems because relativelysmall shading may result in a disproportionate reduction in powergenerated by the system.

The overriding objective of a typical commercial or residential rooftopinstallation is to achieve the highest energy density within a confinedrooftop space. Obviously, the extra spacing lowers installation densityin terms of the number of panels/unit of area. Because of the space,weight and other constraints, the fast-growing commercial segment hasbeen largely bypassing the conventional tracking option.

Today, practically all rooftop-based commercial solar installations arefixed and most of the tracking systems can be found in largeutility-scale ground-based installations in remote areas where space isrelatively inexpensive and abundantly available. Therefore, what isclearly needed is a solar tracking system and method for tracking thesun that can minimize shadowing thrown on adjacent panels and allow formore panels to be placed in a smaller footprint without reducing theamount of efficiency of the system.

SUMMARY OF THE INVENTION

The problem stated above is that maximum efficiency is desirable for asolar collector system or array, but many of the conventional means formaximizing solar energy collection is solar system also createcomplexity and cost. The inventors therefore considered functionalelements of a modular solar collector system, looking for elements thatexhibit interoperability that could potentially be harnessed to provideenergy but in a manner that would not create drag.

Every solar system is propelled by the suns rays, one by-product ofwhich is an abundance of stored energy that can be utilized directly.Most such systems employ solar panels and tilting means to minimizeangle of incidence (AOI) thereby increasing energy savings.

The present inventor realized in an inventive moment that if, duringsolar tracking, modular solar collecting devices could be caused totrack the sun in unison using both synchronous and counter synchronoustracking such that by one or more pivot axis' the panels may be causedto tilt and/or track along those axis', more solar efficiency in solarenergy collection might be realized. The inventor therefore constructeda unique modular system of solar collection devices for rooftops andcommercial installations that allowed minimization of AOI during solartracking thereby increasing solar collection efficiency during the solartracking operation. A significant reduction in work results, with noimpediment to solar footprint or existing solar efficiency ratingscreated.

Accordingly, in an embodiment of the present invention, a method fortracking solar panels is provided comprising the steps of (a) beginninga tracking cycle substantially at sunrise with adjacent tilting panelsall horizontal, (b) tilting the adjacent panels in unison in a firstangular direction toward the rising sun at a tilt rate that just avoidsshading of adjacent panels, (c) reversing direction of panel tilt at apoint that the panels reach either a maximum tilt limited by mechanicaldesign, or the panel surfaces are orthogonal to the rising sun, (d)tilting the adjacent panels in a second angular direction, followingmovement of the sun and keeping the surface of the panels at rightangles to the sun's position, until a point is reached that shadowing isimminent from the angle of the setting sun; and (e) reversing directionof panel tilt again to the first angular direction, adjusting tilt asthe sun sets to avoid shading until the panels are again horizontal.

In one aspect of the method in steps (b) and (e), tilting allows apre-programmed percentage of shading to occur. In a variation of thisaspect, in steps (b) and (e) the tilting allows a pre-programmedconstant percentage of shading to occur. In a variation of this aspect,in steps (b) and (e) the tilting allows a pre-programmed percentage ofshading to occur, and the percentage varies with angle of tilt. In oneaspect the tilting is accomplished in a continuous motion. In anotheraspect the tilting is accomplished incrementally at pre-programmed timeincrements.

In one aspect of the present invention a solar panel system is providedand includes a plurality of solar panels having a length substantiallygreater than a width mounted side-by-side with each panel enabled totilt about along an axis in the direction of the length of the panel, atilting mechanism coupled to adjacent panels, capable of tilting thepanels in either of two rotating directions about the panel axes, and aprogrammable drive control enabled to control the rate and direction oftilt for the panels in unison in a tracking cycle.

The tracking cycle begins substantially at sunrise with the panelshorizontal, the panels are tilted in unison in a first angular directiontoward the rising sun at a tilt rate that just avoids shading ofadjacent panels, direction of tilt is reversed at a point that thepanels reach either a maximum tilt limited by mechanical design, or thepanel surfaces are orthogonal to the rising sun, the panels are tiltedin a second angular direction, following movement of the sun and keepingthe surface of the panels at right angles to the sun's position, until apoint is reached that shadowing is imminent from the angle of thesetting sun, and tilting direction is reversed again to the firstangular direction, adjusting tilt as the sun sets to avoid shading untilthe panels are again horizontal.

In one embodiment the tilting allows a pre-programmed constantpercentage of shading to occur. In another embodiment the tilting allowsa pre-programmed percentage of shading to occur, and the percentagevaries with angle of tilt. In one embodiment tilting is accomplished ina continuous motion. In another embodiment tilting is accomplishedincrementally at pre-programmed time increments.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a block diagram illustrating tilt capabilities of a solarcollection device for maximizing exposure to the sun.

FIG. 2 is a perspective view of a modular solar device includingbrackets for installation.

FIG. 3 is a perspective view of a modular solar device having slotadapters for installation.

FIG. 4 is a side view of a modular solar device illustrating horizontaltilt capability according to an embodiment of the present invention.

FIG. 5 is a perspective view of a standard solar panel installation.

FIG. 6 is a perspective view of a modular device according to anembodiment of the present invention.

FIG. 7 is a perspective view of a modular solar array according to anembodiment of the present invention.

FIG. 8 is an architectural overview of an integrated network for remoteaccess and maintenance of a system of flat-panel arrays.

FIG. 9 is a perspective view of a modular device array according to anembodiment of the present invention.

FIG. 10 is a perspective view of a modular device array including alateral transfer system according to another embodiment of the presentinvention.

FIG. 11 is a perspective view of a flat panel array according to anotherembodiment of the present invention.

FIG. 12 is a perspective view of several gantry robot configurationsaccording to an embodiment of the present invention.

FIG. 13 is a cutaway view of a multi track robot according to anembodiment of the present invention.

FIG. 14 is a cutaway view of a multi-track robot according to anotherembodiment of the present invention.

FIG. 15 is a perspective view of optional hose or cable feeder/tensionerassemblies for use in cleaning operations according to embodiments ofthe present invention.

FIG. 16 is a top view of a robot tracking on a hybrid tracking system1600 according to an embodiment of the present invention.

FIG. 17 is a top view of a robot tracking on a hybrid tracking systemaccording to another embodiment of the present invention.

FIG. 18 is a top view of a robot tracking on a tracking system accordingto a further embodiment of the present invention.

FIG. 19 is a logical block diagram illustrating angle of incidence (AOI)of the sun against a solar array.

FIG. 20 is a block diagram illustrating an angular range of motion(AROM) for a solar panel according to an embodiment of the presentinvention.

FIG. 21 is an elevation view of a modular device illustratinginter-array spacing or separation.

FIG. 22 is a chart illustrating retrograde tracking according to anembodiment of the present invention.

FIG. 23 through FIG. 27 are block diagrams illustrating two solar unitsin various states of solar tracking in unison.

FIG. 28 is a perspective view illustrating two array configurationoptions according to an embodiment of the present invention.

FIG. 29 is a perspective view of a single sub-frame section of linkableframe component of FIG. 28.

FIG. 30 is a partial view of a frame member according to an embodimentof the present invention.

FIG. 31 is a perspective view of frame member of FIG. 30 showing outerskin and multiple tilt mechanisms.

FIG. 32 is a block diagram illustrating basic tracking module componentsof a tracking module.

FIG. 33 is a partial view of a frame member of the modular solarcollecting system of the present invention.

DETAILED DESCRIPTION

The inventor provides a modular solar collector system that has dualsun-tracking capabilities, self-inspection and self-cleaning maintenancecapabilities, and other general improvements over standard art systemsfor residential and commercial use. The present invention is describedin enabling detail using the following examples, of which may show morethan one useful embodiment of the present invention.

The terms solar panel and solar module are commonly used interchangeablyin documents that describe conventional solar collecting systems.However, in this specification, and to avoid confusion, the termsmodular solar collecting device or simply modular device shall be usedto reference a fully-functioning solar collecting unit enclosed in arigid sub-structure with full electrical and/or thermal connections. Themodular device of the present invention two or more such devicescomprising a modular solar collecting system, may be functionallysimilar to solar panels/modules in the conventional system with respectto solar collecting technologies and may encompass, but may not belimited to, mono or poly-crystalline silicon photovoltaic (PV),thin-film-based PV, concentrator PV (CPV) and concentrating solarthermal (CST) technologies.

Modular Solar Collecting System with Linking Hardware and Device TiltingCapability

Modular devices of the present invention may or may not be longer inlength than conventional solar panels, but are likely to be narrower inwidth compared to their conventional counterparts. Wider devices havelarger axial tilting radii requiring greater mounting heights for groundclearance, which is a problem in the art that the present invention isdesigned to overcome. For the purposes of this specification, anintegrated group of modular devices comprises a modular subsystem andone or more of installed modular subsystems comprise a modularsub-system array. A typical solar installation, whether commercial orresidential, has one or more arrays.

FIG. 1 is a block diagram illustrating tilt capabilities of a solarcollection device for maximizing exposure to the sun. To attain themaximum efficiency in collecting solar rays, the surfaces of solarcollecting devices should be orthogonal to the sun at noon when itsintensity peaks. In reality however, the orientations of installationsurfaces of solar systems are rarely optimal. Tilting compensates forpoor device orientation (steep/shallow sloping surface or offset fromtrue south in the northern hemisphere). Therefore a capability oftilting the devices can work to correct offset angles (θ).

A solar collecting device 101 has panels 104 that tilt horizontally tooptimize the exposure to sun 103. A solar collecting device 102 hassolar panels 105 that compensate or adjust for meridian of sun 103.Therefore a modular solar device has panels that may tilt horizontallyand vertically to optimize exposure to the sun thus maximizing theefficiency of the unit.

FIG. 2 is a perspective view of a modular solar device includingbrackets for installation. FIG. 3 is a perspective view of a modularsolar device having slot adapters for installation. Referring now toFIG. 2, a modular device 201 may be manufactured of 2×12 silicon-basedPV cells 205. Device 201 includes mounting brackets (202), one per side.Mounting brackets 202 include upper and lower pivot points 203 and 204respectively. A dashed line is illustrated in this example andrepresents the tilt axis of the device.

Referring now to FIG. 3, a modular solar collecting device 301 isillustrated and includes a uniform coating 303 of thin-film PV. Device301 includes slot adapters 302, one at each end in this example. Slotadapters 302 may be of various shapes and sizes. The slot adapters aremated to slot receptacles, (not illustrated) on a frame component toestablish mechanical connection. Carbon composites or other light weightmaterials may be used in manufacture of the modular device'ssub-structure. Individual modular devices may or may not be equippedwith dedicated micro-inverters (not illustrated) that convert DC modulardevices into AC modular devices.

In one embodiment a modular device with tilting capability comprises asection of extruded rectangular tubing having a top surface, a bottomsurface and two side surfaces. Photovoltaic or other types of solarcells, PV coatings or a combination may be applied to the top surface,the bottom surface, and the side surfaces in order to improve overallefficiency by harvesting power from indirect light either reflected orrefracted to the bottom and side surfaces of the device. In one aspectof this configuration thin film PV coatings may be used on the sides andbottom surface of the modular device. As costs continue to come down forthin film coatings, the practicality of employing them to enhanceefficiency by applying them on secondary device surfaces may become morepractical.

In one embodiment a modular subsystem includes multiple modular solarcollecting devices, a frame that holds the modular devices and hardwarethat connect individual modular devices together and provides pivotpoints. A frame (not illustrated here) may be as simple as a rectangularbox with angled cutouts for “hanging” modular devices at a desiredangle. In another embodiment a frame may include pivot points and atilting mechanism incorporated within the thickness of its wall. In a“plug and play” embodiment, modular devices may be pushed into slottedand pivoted receptacles built into the sides of a frame. The simpleinsertion may lock the devices in place and establish both mechanicaland electrical connections.

Frames provided to contain modular devices may be made of any one of anumber of hard man-made/synthetic materials such as steel, aluminum,fiberglass, carbon composite, or plastics, depending in part on cost,weight and durability. Frames may or may not be manufactured usingmolding or extrusion method. Pre-drilled holes, notches and otherprovisions may facilitate easy fastening to various types ofinstallation surfaces. Pre-fabricated frames may be available indifferent lengths to hold fixed numbers of modular devices, but two endplates may be identical. Made-to-order frames, however, may accommodateany number of modular devices as required by end-user.

In a conventional system solar collectors or cells, for example, aredirectly installed on a simple rack structure. In the modular system ofthe present invention, it is preferable to first mount a number ofmodular devices in a rigid rectangular frame that mechanically connectsthem together in a parallel “louver-like” arrangement. The mechanicalconnections allow them to tilt in sync as a single integrated unit.Electrical and thermal integration may be also made at this point. Theframing and the interconnections transform these modular devices into amodular subsystem that is ready to be installed. The modular subsystemis comprised of modular solar collecting devices, a frame that holds themodular devices and hardware that connect individual modular devicestogether and provides pivot points.

FIG. 4 is a side view of a modular solar device 401 illustratinghorizontal tilt capability described further above according to anembodiment of the present invention. Modular solar device 401 containsmultiple modular solar collecting devices 405, which may be analogous tosolar devices 201 described further above in this specification.

In this example, devices are mounted on a frame 402 by the upper pivotpoints allowing the devices to tilt axially (lengthwise). The lowerpivot points may be connected to a tilt bar or device connection bar403. The device connection bar 403 enables a synchronized tilt of theinstalled devices to an angle that is appropriate for maximizing energycollection according to position of the sun.

FIG. 5 is a perspective view of a standard solar panel installation.FIG. 6 is a perspective view of a modular device according to anembodiment of the present invention. Referring now to FIG. 5 and to FIG.6, the two arrays illustrated underscore the difference between theconventional and modular systems. Referring now to FIG. 5, aconventional solar array 501 is illustrated. Solar array 501 comprisesan aggregation of panels 503 onto a racking structure 502. Rackingstructure 502 is provided at a fixed elevation in order to orientate thearray toward the sun. However, this tilting method is only practical forinstallations on flat surfaces. For sloped rooftop installations wheresolar arrays need to be “flush” with the roof, such elevation is usuallynot an option. As a result, a majority of conventional rooftopinstallations face less than ideal angles and therefore are lessefficient in collecting energy.

Referring now to FIG. 6, a modular solar array 601 is provided and maybe installed directly on the installation surface without any rackingstructure like racking structure 502. To install a modular array, blankframes such as a frame 602 may be first positioned, shimmed and fastenedto the installation surface. Then modular devices such as devices 201may be installed inside one-by-one until the frames are filled. Finally,the tilt adjustment may be made within the frames. This installationprocess may reduce labor cost. The low-profile mounting and tiltingmeans superior installation flexibility.

So far in this specification tilting of solar collection devices hasbeen illustrated as a way to optimize the angle of incidence in contactwith the solar rays. While tilt adjustments may be sufficient for somesolar installations, a much greater level of efficiency may be obtainedthrough passive and or active tracking of the Sun. Tracking for thepurposes of this specification shall mean the continuous following ofthe sun to maintain the optimal angle of the suns rays against a modulardevice as long as possible. The modular subsystem of the presentinvention includes a built-in synchronized tilting capability that makesolar tracking easily attainable. For example, a tracking module (notillustrated) installed over one of the end plates of the system mayconvert any modular subsystem into a low-profile tracking system that ispractical even for small rooftop installations.

In such a system, inside the tracking module, tracking motion may beattained in a number of ways including but not limited to using anin-line actuator or motor and screw set, or perhaps a transverse-mountedmotor and hinged arm set. Such a tracking module may also house motioncontrol electronics as well as a wired or wireless network adapter cardallowing its status to be viewed by a remote computer. The maximumlength of tracking modular subsystem should be limited only by thesize/power of the actuator or motor used.

To install a solar array using the system described here, an installermay first select different combinations of frames (various types andsizes including custom sizes) that best suits system requirements orneeds and then populates those frames with a like different combinationof modular devices of his/her choosing. Later, a tracking module may beadded to the system by plugging it into the system. Such plug and playinstallation allows the module to function seamlessly and harmoniouslywith the rest of the system qualifying the system as a true modularsystem.

FIG. 7 is a perspective view of a modular solar array 701 according toan embodiment of the present invention. In one embodiment, modularity ofthe system may extend beyond the boundaries of subsystem frames. Array701 has mechanical linkages (not illustrated) established betweenmodular subsystems that allow all of the modular devices such as devices702 and 703 in the array to tilt together in unison. Devices 702 arethin film-based while devices 703 are silicon-based. Other types mayalso be added into the installation without departing from the spiritand scope of the present invention.

In one embodiment the linkage may be serially connected (lengthwise asshown below). In another embodiment the linkage may be parallel (side toside). A combination of the two may also be implemented withoutdeparting from the spirit and scope of the present invention. A trackingmodule 704 is provided at one end of one modular subsystem. Trackingmodule 704 enables the entire array to track the sun. Although notspecifically illustrated here, the physical connection among the modularsubsystems may be accomplished in multitudes of ways. For example, inone embodiment is a metal extension strip that clips on between twoadjacent device connection bars that control tilt angles through cutoutson end-plates. In another embodiment, electrical and other types oflinkages between modular subsystems may be simultaneously established.

It will be apparent to a skilled artisan that the embodiments describedabove are exemplary of inventions that may have greater scope than anyof the singular descriptions. There may be many alterations made inthese examples without departing from the spirit and scope of theinvention. For example, different modular subsystems may have modularsolar collecting devices of different lengths and widths. One or moremounting brackets of many shapes, sizes and materials may be implementedat various positions. Tilting of modular arrays can be achieved in avariety of ways within a frame. Motors or actuators for tracking may beintegrated with modular subsystems. A tracking drive may have an in-lineactuator or AC/DC motor and may also use components such as gears,screws, levers, pulleys, belts, chains, or cords for power transmissionwithout departing from the spirit and scope of the present invention.

Self-Monitoring, Cleaning, and Maintenance

In addition to the useful embodiments describing a modular solar arrayabove, the inventor further provides a system and methods for automatedself-monitoring and cleaning and provision of other maintenance needsfor a solar array or for another type of flat panel array such as glassor other hard and smooth surfaces not necessarily limiting to modularsolar arrays. The present invention is described in enabling detailusing the following examples, which may include descriptions of morethan one embodiment of the invention. In this specification, a flatpanel shall mean a large flat surface of various dimensions made ofglass, metal, or any other hard and smooth substances. Examples of flatpanels include, but are not limited to solar panels and glass panels. Anarray shall mean a cluster of flat panels laid side by side that isphysically separated from other clusters. Installations such as solarfarms and glass façades of buildings may have any number of arraysgreater than or equal to one.

FIG. 8 is an architectural overview of an integrated network 800 forremote access and maintenance of a system of flat-panel arrays. Network800 includes an installation of multiple photovoltaic flat-panel arrays805 (a-n). Each array 805 (a-n) includes a robot 812 and a sensor unit806. A robot 806 may be a cleaning robot equipped with delivery hosesfor delivering a cleaning solution to the flat-panels, which are solarpanels in this example. Modular solar devices may be substitutedtherefor in one embodiment of the invention. Robot 8121 may also includean optical component such as a camera eye for enabling a visualinspection of the surfaces of the flat panels in each array. Each devicearray 805 (a-n) is accessible through a switching facility 808.

The multiple device arrays share a single hardware component group 810in this example. Hardware component group 810 includes a compressor, anumber of valves and manifolds, and a water pump. It is noted that group810 may include other shared components without departing from thespirit and scope of the present invention. The maintenance activity iscontrolled by a single intelligent controller 807. All communications toand from each array 805 (a-n) are routed through switching facility 808as described above. Ethernet cables might be used form the singleintegrated network 800 to monitor, inspect, analyze, and maintain theentire installation in the optimal operating condition.

As described above, each array 805 represents a network node on network800. Each array may have a network identification and network address.Each array 805 may include multiple solar panels 813, a dedicated robot812, and a sensor unit 806. Sensor unit 806 may include a digitalsurface temperature probe for calibration and a current/voltage meterfor performance metrics (sub-devices not illustrated). The measurementsmay be made for the array as a whole or on a panel-by-panel basis. Thesensor unit may be replaced by certain smart micro-inverters thatfacilitate real-time data output.

Shared hardware 810 may include an air compressor, water pump and asystem of digitally-controlled valves and manifolds that delivers airand liquid to robots 812 as directed by the controller via a hardwareinterface 809. Although not specifically required to practice thepresent invention, a firewall-equipped router and modem 804 may beprovided and then connected to the Internet illustrated herein asInternet cloud 801 to enable an administrator to monitor and control thenetwork remotely via a computer 802 or a smart phone. An optionalwired/wireless wall-mounted display console or display monitor 811 maybe used locally for similar purposes.

Although not required, controller 807 may serve as the brain for theentire distributed network. It may be equipped with an embedded singleboard computer, flash drive for data storage, and intelligent digitalservo-drive for each axis of motion in the network. Controller 807 maybe in constant communication with individual robots 812, sensors andshared hardware system 810, sending commands and receiving data. Smartnetwork configuration software (SW) 814 may be provided on a suitabledigital medium to be executed there from to auto-detect a new robot oraxis and launch a SW configuration wizard. In this example the SW isimplemented on the controller unit 807.

In one embodiment network 800 includes remote access capability throughthe Internet 801. In this case a GUI 803 may be accessed from a Website(not illustrated) using a remote computing appliance such as Laptopcomputer 802. GUI 803 may be provided so that a user may configure themaintenance of the system remotely through the Internet or some otherdigital network accessible to the World Wide Web (WWW). A suite ofapplications and widgets (not illustrated) may be available viaWeb-based GUI for functions such as real-time condition/powermonitoring, surface inspection, trend analysis, and other types of userqueries and/or inputs.

In one embodiment of the invention controller 807 may monitor real-timedata from the sensor units 806 to gauge the health and performance ofeach panel in each array. The controller may also splice together stripsof thermal images taken from the imaging module of robot 812 (moredetail latter in this specification), assign a cleanliness index, andmake interpretations of any anomalies or potential issues relative toeach inspected panel. Problems may be identified and possible remediessuggested by the controller with the aid of the ability tocross-reference and analyze two sets of real-time data with previouslystored calibration and mined historical data.

The outcome of the analysis as suggested immediately above may result inan immediate initiation of an automated response such as “blow away theleaves on Panel #7” or “wash the entire array”). In one embodiment areport is generated and sent to an administrator that summarizes themaintenance problems and suggestions. This option may be pre-determinedby the user. Time stamp and the associated parametric values may belogged and reported to the administrator for each automated response.

Cleaning and surface inspections may be scheduled in a number ofdifferent ways. In one embodiment a network administrator of thenetworked system may set a default maintenance frequency using acomputer (802), a smart phone, or a wall-mount console 811. Such asetting may such as a command for cleaning, for example, dry cleanpanels two times per week and wet clean the panels once per month. Manyother examples are possible. In one embodiment controller 807 may deviseand implement its own flexible cleaning schedule on an “as needed”basis. Such a decision may be determined by real-time sensor data, imagedata, equipment status, and other performance metrics, as well as theweather forecast retrieved from the Internet.

In an embodiment utilizing intelligent digital servo drives, the systemmay be enabled to monitor the state and performance of each motor. Suchinformation, in conjunction with encoder data and other sensor data maybe used to predict problems that may arise in robot 812 or that mightarise in other hardware before an actual failure event materializes.Such predictive maintenance capability could render routine scheduledrobot maintenance obsolete.

FIG. 9 is a perspective view of a modular device array 900 according toan embodiment of the present invention. Modular device array 900 may benetworked with other similar or dissimilar arrays. In this example theflat panels in array 900 are modular solar collecting devices. In oneembodiment of the present invention, array 900 includes a robot system901 including a gantry 902 that glides on two parallel but opposingtracks 905 situated at opposite ends of array 900. Gantry 902 serves asa platform supporting a cleaning module 903 analogous to module 812described previously. Gantry 903 also supports an imaging module 904.

Cleaning module 903 is enabled to track back and forth over the width ofarray 900 along the direction of the double arrow along side gantry 902.Hoses and/or cables (not illustrated) may enter cleaning module 903 orrobot 901 from one end of gantry 902 or they may be tucked underneaththe gantry along its entire length. Gantry 902 may track back and forthover the entire length of array 900 supported on tracks 905.

In use the system divides work into manageable portions corresponding tothe functional width of the modules. Cleaning module or robot 903 maycontinuously sweep over a strip of contiguous panels horizontally orvertically without stopping at the edge of each panel. At the edge of anarray, the cleaning/imaging modules slide along Gantry 902 while therest of the robot stays stationery before the sweeping motion resumes inthe reverse direction. The bi-directional movement of the platform iscoordinated with the side-to-side sliding movement of the modules untilthe compound motions sweep over the entire surface of an array. It isimportant to note herein that the mechanical reach of the roboticimaging and cleaning modules are such that full side-to-side travel andfull front to rear travel is available to cover an entire modular devicearray.

FIG. 10 is a perspective view of a modular device array 1000 including alateral transfer system according to another embodiment of the presentinvention. Device array 1000 include multiple flat panels orientated ina lengthwise direction instead of along the width of the array aspreviously illustrated above with respect to FIG. 9. In this example, arobot 1001 includes a gantry 1002 that has the same or similar width asthe flat panels, which are modular solar collecting devices in thiscase. This particular configuration may be useful in situations wherethe span of the array is very wide. A lateral transfer system (LTS) 1003is provided at one end of array 1000. LTS 1003 consists of a lateraltransfer vehicle (LTV) 1004, a guide channel 1005, and additional gantrytracks 1006 located under the gaps between panels.

LTS 1003 enables lateral robot movement along guide channel 1005perpendicular to the direction of travel over panels to adjacent rows.The width of gantry 1002 may also be any multiple of the width of theflat panels. LTV 1004 may have built-in track extensions (1007) that aredesigned to line up with the main tracks to allow robot 1001 to roll onor to roll off of a next array track without a pause or a transitionalstep. LTV 1004 may be a self-propelled vehicle with an onboard motor.LTV 1004 may move along its own track on a side of guide channel 1005,or may be a passive vehicle pulled by a fixed motor mounted at the endof the guide channel. A reel 1008 may be provided and attached to LTV1004 to ensure automatic alignment and release of supply hoses to therobot through a feeder/tensioner (not illustrated) mounted on robot1001. In this example, the cleaning module and camera travels laterallyback and forth over the width of the panels and lengthwise along theentire array.

FIG. 11 is a perspective view of a flat panel array 1100 according toanother embodiment of the present invention. Array 1100 has very narrowpanels and includes a gantry robot 1101 that does not require anysliding modules. Array 1100 includes a lateral transfer system (LTS)1102 located at one end of the array. LTS 1102 enables lateral robottransfer between rows and columns of the array depending on theorientation of the panels. This configuration may be suitable for arraysof long and narrow panels with gaps in between. The networked system maybe configured in multitudes of different manners, depending at least inpart on the size, shape and underlying support structure of the array.

FIG. 12 is a perspective view of several gantry robot configurationsaccording to an embodiment of the present invention. A gantry robotconfiguration 1200 includes a gantry robot 1201 with a cleaning module1203 and an imaging module 1204. Other illustrated configurationsinclude gantry robot configuration 1208 and gantry robot configuration1209. All of these configurations are possible variations of gantryplatform 902 described further above with respect to FIG. 9. Eachplatform has a payload that slides side-to-side along the gantry span.Common payloads may include a cleaning module 1203 and an imaging module1204. Configuration 1208 does not include an imaging module.

Gantry robot 1200 includes flanges 1205 located at the ends of thegantry. These flanges may be utilized to mount motors and wheelassemblies (not illustrated). Although the robots may have sophisticatedonboard sensors and data gathering capabilities, intelligence does nothave to reside within the robots in the networked system, but in aremote controller elsewhere in the network.

One of the most critical goals for the networked system may be along-term unmanned operational capability. To achieve such a goal, thecleaning module may or may not use supplies or consumables such asmopping pads, wiping pads, or cleaning solutions that have to bemanually replaced or replenished at each array or robot end. At leasttwo separate cleaning modes might be required to achieve efficientcleaning. For example, a dry cleaning mode and a wet cleaning mode maybe provided. The cleaning module may also use a special cleaningsolution with active enzymes to breakdown chemical bonds and dissolve“baked-in” bird droppings and the like.

In one embodiment of the invention an air knife 1206 is provided andadapted to lay down a laminar air flow for blowing off debris from anarray. In another embodiment multiple spray nozzles 1207 are providedand adapted for wet cleaning by spraying a cleaning solution onto thetarget areas of an array. A combination of the two may providenon-contact cleaning using an uninterrupted supply of air and liquidfrom a central supply system. Air knife 1206 uses a high intensity,uniform sheet of laminar airflow to blow off liquid or debris. Cleaningmodule 1203 may deploy different tools for different cleaningsituations. Air knife 1206 may be sufficient for dry cleaning. In oneembodiment nozzles 1207 may first spray liquid solution on the targetarea. Then the liquid may be allowed to sit or soak for a period oftime. Air knife 1206 may be used to blow off the remaining debris afterthe cleaning solution has broken it up.

In one embodiment, cleaning module 1203 may include a built-in steamgenerator that ejects stream through the nozzles to remove oil-basedparticulates and other sticky particulates. In an alternate embodimentthe cleaning module may utilize a rotating cleaning head with wipingblades or brushes (not illustrated) in place of air knife 1206. Afterspraying and soaking, rotating heads may have to be lowered to make aphysical contact with the panel surface. Blades or brushes may be madeof rubber, plastics or other durable man-made materials.

In one embodiment of the present invention, an imaging module such asmodule 1204, for example, may play a critical role in panel inspection,performance monitoring and condition-based cleaning. For example, it mayscan panel surfaces in infrared or other bands of electromagneticspectrum to identify anomalies, check for cleanliness state and tocharacterize panels. Thermal images may be highly useful in identifyingand diagnosing problems and may assist the system in solutionrecommendation. The scanned strips of images may be sent to controllerfor analysis and storage.

It will be apparent to the skilled artisan that the apparatus forcleaning and inspecting panel surfaces termed a robot cleaning module orpayload may vary in length, shape, and capability without departing fromthe spirit and scope of the present invention. For example, cleaningmodule 1203 may be annular or rectangular. Gantry 1202 may berectangular or annular. Many differing configurations are possible. Thekey aspect is the capability of the robotic component to inspect, reportfindings, and then to clean the flat panel surfaces accordingly.

FIG. 13 is a cutaway view of a multi track robot 1300 according to anembodiment of the present invention. Multi-track robot 1300 includes agantry platform 1302. Payloads provided in this example include acleaning module 1303 with cleaning nozzles and or an air knife, and animaging module 1304. The wheels of gantry platform 1302 run on tracks1313 situated below panels 1314. In this embodiment the width of gantryplatform 1302 matches the spacing between each row or column ofsupported flat panels 1316.

Flat panels 1314 are supported by support beams 1315 and by cross beams1316 situated underneath the panels and comprising the framing structurefor the array. In this embodiment robot 1300 is suitable for modularsolar arrays. In one embodiment robot 1300 is driven along track 1313 bya main motor 1305 attached to a pinion gear 1306. Pinion gear 1306together with guide wheels on the opposite side of the track and theirhousing, forms a driving wheel assembly 1307. An auxiliary motor 1308 isprovided in this example and is adapted to power a linear drivemechanism 1309. Linear drive 1309 slides the gantry payloads along thespan of the gantry. On the left leg of gantry 1300, a non-driving wheelassembly 1310 is provided and is adapted to guide the robot along thetrack.

The wheel assemblies are mounted perpendicularly to the gantry legs tofit in the limited space between the panels and the cross-beams. Theentire drive mechanism is hidden under the panels. A feeder/tensioner1311 is provided and adapted to assist robot pull hoses and/or cables1312 from a reel underneath each array. A hose guide 1317 aids inchanging the direction of the hoses.

FIG. 14 is a cutaway view of a multi-track robot 1400 according toanother embodiment of the present invention. Robot 1400 includes acleaning module 1403 and a gantry platform 1402. In one embodimentgantry robot 1400 does not include gantry legs. Instead the wheels andmotors thereof are mounted on flanges extending perpendicularly from thelengthy of the gantry. The wheels are positioned to run on the inside ofthe channels extending through the system at either end of each array.The cleaning module and a feeder tensioner for hose/cable assistanceshare the same axis. This present configuration is useful for a buildinghaving long vertical glass flat panels, for example.

FIG. 15 is a perspective view of optional hose or cable feeder/tensionerassemblies for use in cleaning operations according to embodiments ofthe present invention. A feeder/tension assembly 1501 is provided and isillustrated as an optional assembly for supporting hose/cable managementduring a cleaning operation.

Assembly 1501 may be used for under-the-panel routing, where hoses orcables are routed from a reel 1502 attached to the system, through ahose guide 1503, and then through a feeder/tensioner 1504 installed onone of the gantry legs. The routed hoses enter the cleaning module 1505on one of the gantry legs, before entering a cleaning module 1505.

A feeder/tension assembly 1506 is provided and is illustrated as anoptional assembly for supporting hose/cable management during a cleaningoperation. Assembly 1506 illustrated on the right hand side as viewedmay be suited for over-the-panel routing.

Hose or cable travel from a reel 1507 to a swiveling feeder/tensioner1508, then directed to a cleaning module 1509. Swivelingfeeder/tensioner assembly 1508 may sit on its own track at the top of anarray allowing a robot to simultaneously tow and draw hoses from it overthe flat panels.

In a preferred use embodiment, as a robot scans and or cleans a flatpanel surface of an array, a spring-loaded rotary hose feeder/tensionerwith an auxiliary hose reel such as those illustrated and described inthis example, draws hoses/cables from a main reel and maintains them inuniform tension while dampening stress and time lag as it overcomesinertia. A right amount of tension may prevent snag, tangle or kink ofthe hoses. A built-in tension sensor (not illustrated) may be providedtrigger an emergency stop if the tension on hoses and/or cabling exceedsa preset limit. An external hose guide orientates hoses toward thefeeder/tensioner at all times. It is noted herein that tracks may be ofvarious shapes and sizes. Tracks may be manufactured of any one of anumber of hard man-made or synthetic materials such as steel, aluminum,or plastics, depending in part on cost and durability. Tracks may belaid under, between, or on the sides of flat panels.

FIG. 16 is a top view of a robot tracking on a hybrid tracking system1600 according to an embodiment of the present invention. Hybridtracking system 1600 includes a deviation tolerant non-driving wheelsassembly 1604 and a driving anti-torque wheel assembly 1609. Annularinset 1601 illustrates a double-sided hybrid track made of a gear racksandwiched between two flat plates. This track embodiment includes atoothed rack side 1602 and a flat rail side 1603. The particularconfiguration allows for a pinion gear such as pinion gear 1611 on oneside and wheels/rollers 1612 on the other. The hybrid tracks are mountedhere on their sides directly on the cross-beams that run below panelsupport beams.

Because the robots ride on rigid tracks, it is important that the tracksare substantially parallel with spacing sufficient to prevent therobot's wheels from getting jammed between them. However, when thetracks are installed in the field, some deviations (θ) should beexpected. One of the methods to compensate for the lack of precision andmake the drive system more robust may be to make at least one of the twowheel assemblies “deviation-tolerant” such as assembly 1604 above.

On the non-driving side, the entire wheel assembly 1604 is mounted onthe flange of the gantry 1605. The assembly includes two articulatedlinks 1606. A coil spring (not illustrated) occupies the wheel housingalong a common pivot axis 1607. The torsion of the spring pushes twowheels/rollers 1608 against the flat side of the track. When narrowingof the track occurs, the housing pivots and the angle between the linksalso narrow and vice versa. Such scissor-like action maintains constanttraction on the wheels.

On the driving side, anti-torque driving wheel assembly 1609 includes amotor 1610. Motor 1610 is adapted to turn pinion gear 1611 against therack side of the track. Twin wheels/rollers 1612 make intimate contactwith the track from the rail side and counter-balance the momentumproduced by motor 1610. A triple-pronged wheel housing 1613 is providedthat bounds pinion gear 1611, motor 1610, and wheels 1612 together on aflange 1614 extending from one of the gantry legs. The robot tracks inthe direction of

FIG. 17 is a top view of a robot tracking on a hybrid tracking system1700 according to another embodiment of the present invention. In thisexample a left wheel assembly 1701 is provided as a non-driving wheelassembly. Wheel assembly 1701 includes a boomerang-shaped wheel housing1702. Wheel housing 1702 has a pivot point at center 1703. Wheel housing1702 pivots at center point 1703 and may move freely along slot 1704.Slot 1704 is cut into flange 1712 extending out from one of the gantrylegs.

In use, a tension/compression spring (not illustrated) installed betweenwheel housing 1702 and the flange pushes the housing and its twinwheels/rollers 1705 outward against the flat side of the track,continuously adjusting to narrowing or widening of the track spacing ina deviant tolerant manner as described further above.

On a right wheel assembly 1706, a boomerang shaped wheel housing 1707holds one large pinion gear 1710 and two small pinion gears 1711together in mounted position on flange 1708 extending from the gantry. Amotor 1709 mounted on flange 1708 turns large pinion gear 1710 to movethe robot relative to the rack side of the track in the direction of thedirectional arrow.

FIG. 18 is a top view of a robot tracking on a tracking system 1800according to a further embodiment of the present invention. In thisembodiment the hybrid tracks utilized in the previous examples arereplaced by a C-shaped channel 1801 as shown in the annular inset takenfrom or expanded from section line 1801. A driving wheel assembly 1806is provided and includes two small wheels 1807, and a large wheel 1809held together in mounted position by a boomerang-shaped wheel housing1808 and a flange 1811.

A non-driving wheel assembly 1802 is provided and includes abutterfly-shaped wheel housing 1803. Wheel housing 1803 has two linksjoined and pivoted at the center where it mounts to flange 1804. Atorsion spring (not illustrated) installed between them pushes two ofthe wheels 1805 against the inside wall of the channel and the other twowheels 1805 against the opposite wall of the channel. The asymmetricshape of the links allows the wheel assembly to expand and fold to matchthe width of the channel while avoiding any contact between them.

Driving wheel assembly 1806 works in a manner similar to the non-drivingwheel assembly except that it has three wheels instead of four wheels.The torsion spring on the common axis pushes twin wheels/rollers 1807 atthe end of an articulated housing 1808 toward the inner wall of theC-shaped channel while the larger main wheel 1809 at the center pushesoutward as well. This particular wheel assembly configuration may alsobe able to adjust itself to different channel widths, but in order toresist the moment produced by a motor 1810 mounted on flange 1811, thetorsion spring may have to be fairly stiff. The motor urges the robotalong the channel in the direction of the arrow. To remove either wheelassembly 1802 or 1806 from the respective channel, it has to be foldedusing a tool and a pin inserted through a hole (not illustrated) to lockthe position before removal.

It will be apparent to a skilled artisan that the embodiments describedabove are exemplary of inventions that may have greater scope than anyof the singular descriptions. There may be many alterations made inthese examples without departing from the spirit and scope of theinvention. For example, each robot may have an on-board controller.Robots of many different shape, sizes and configurations may be made ofmany different materials. Different versions of cleaning modules mayhave varying widths and effective coverage areas that may alter thenumber of passes and sweep sequence required to cover a whole panel orarray. Certain embodiments of cleaning modules may utilize other contactand non-contact cleaning methods such as acoustic technologies. Imagingmodules may adapt an alternate surface scanning technologies such aslaser or electromagnetic bandwidths other than infrared. Sensor modulesand other additional modules may be added on the payload list withoutdeparting from the spirit and scope of the invention. Differentconfigurations of wheels may run on tracks of many shapes, sizes andmaterials. Air and liquid supplies and delivery systems may be installedat each array instead of at a central location. There are manypossibilities.

Retrograde Tracking for Solar Panels

In this specification a solar device refers to a discrete solar energycollection component. A solar device may be a solar photovoltaic (PV)cell, a chemical coated/treated substrate or heat-absorbing surface andmay use crystalline silicon PV, thin film, concentrating solar, solarthermal or any other solar technology. The terms solar panel (a.k.a.solar module) is defined as a collection of one or more solar devicesthat are mounted together on a common base with built-in conduits fortransferring energy to a larger energy storing/transmitting system ornetwork. Solar array means a group or cluster of solar panels. Trackingpanel, tracking array or more generic tracking unit refers to one ormore of solar panels moving in unison on a common tilting plane.

FIG. 19 is a logical block diagram illustrating angle of incidence (AOI)of the sun against a solar array. Regardless of the technology used,solar panels are most efficient when the angle of incident (AOI) isminimized as is illustrated herein. That is to say when the rays of thesun come in at an angle that is normal to the energyabsorbing/converting surface then the angle is minimized. The generalrule is that the larger the deviation from zero AOI, the smaller theamount of energy is available to the solar collection process.Therefore, it is a desire that solar tracking systems have minimal AOIas long as possible to maximize energy conversion efficiency.

Further to the above, commercial tracking systems may be either singleaxis or double axes systems. In a single axis system, panels face thesun and follow it as it rises from the east and sets in the west. Thisaxis (FIG. 19) running north-south is often referred to as the primaryaxis. In addition to this daily east-west motion, a double-axes trackingsystem has a secondary axis that is used to adjust its tilt angle over aone year cycle to adapt to the seasonal variations of the sun resultingin higher elevation in the summer and lower in the winter.

FIG. 20 is a block diagram illustrating an angular range of motion(AROM) for a solar panel according to an embodiment of the presentinvention. Tracking systems have angular range of motion (AROM). In thisexample, AROM equals to two times θ representing the tilt limit of thepanel in either direction measured from the horizontal plane (brokenrectangular boundary) in the east-west direction. Cross-shading, a termcommonly used in solar jargon, refers to a condition that causessystemic shading of adjacent tracking units. It usually occurs at lowsun angles due to insufficient inter-array spacing.

A typical tracking system known in the art uses synchronous motion (SM)where the panels always face the sun and tilt at the same constant ratein sync with the sun. In contrast to this standard method, the termcounter-synchronous motion (CSM) coined by the inventor refers to aunique tilt motion activated in the opposite direction relative to thesun either toward or away from the sun. The angular trajectory is still,however, dependant on the position of the sun during tracking.

FIG. 21 is an elevation view of a modular device illustratinginter-array spacing or separation. The width of tracking unit is definedas the width seen along the direction of the primary axis. The distancebetween adjacent primary axes defines inter-array spacing or separationas shown in FIG. 21.

Limitations of Conventional Tracking Systems

It is a well established fact that tracking solar arrays can producesubstantially more energy (watts/panel) compared to fixed arrays of thesame type and capacity. This difference is most pronounced for thoseusing crystalline silicon PV technologies, where a single-axis trackingsystems could add up to 30% more energy. However, there is a penaltyinvolved. When one side of array is raised at low sun angles, the arrayscast larger shadows and require greater separation compared to theirfixed counterparts. Again, this penalty is costliest for crystalline PVsystems because relatively small shading may result in adisproportionate power reduction.

The overriding objective of a typical commercial rooftop installation isto achieve the highest energy density within a confined rooftop space.Obviously, the extra spacing lowers installation density in terms of thenumber of panels/unit of area. Because of the space, weight and otherconstraints, the fast-growing commercial segment has been largelybypassing the conventional tracking option.

Today, practically all rooftop-based commercial solar installations arefixed and most of the tracking systems can be found in largeutility-scale ground-based installations in remote areas where space isrelatively inexpensive and abundantly available. The tracking methoddescribed below addresses these shortcomings and may enable practicalrooftop-based tracking solutions in the future.

Retrograde Tracking

Unlike the conventional tracking systems that track the sun from horizonto horizon exclusively using synchronous motion (SM), retrogradetracking is a hybrid strategy incorporating a second element, a variablespeed counter synchronous motion (CSM), in a seamless manner.

FIG. 22 is a chart illustrating retrograde tracking according to anembodiment of the present invention. In retrograde tracking, SM is usedwhen the sun is within the system AROM (center region in FIG. 22) andCSM is used when the sun is outside of it (regions adjacent to centerregion in FIG. 22). Retrograde tracking requires a single-axis east-westretrograde motion, but a secondary axis may be combined to provideseasonal tilt adjustments in the north-south direction.

Successful implementation of retrograde tracking requires a properinter-panel/array spacing that is a function of the panel/array widthand their AROM. In an optimized embodiment, this is the minimum distanceat which no cross-shading is possible when the sun is within the AROM.This arrangement creates an interference-free zone for SM (the centerwedge).

Over the 12-hour span, the vector normal to the panel surface(dashed-line) sweeps the center AROM region twice (swings right, left,and then back to right) without crossing into the adjacent regions. Thatis to say both SM and CSM tracking take place within this center region.This pendulum-like motion is traced using a timeline at the top of thechart. The numbers on top of the chart represent hours in a 24-hour timeperiod. The order of steps is as follows:

-   -   1) Panels are in the horizontal standby position as the sun        rises from the east.    -   2) Panels gradually tilt east toward the sun until it reaches        their tilt limit. (CSM tracking)    -   3) When the tilt limit is reached at the border, AOI is zero and        panels reverse direction and start tilting in sync with the sun.        (SM tracking)    -   4) When the tilt limit is reached again on the opposite side,        the panels decouple from the sun and reverse direction once        again to move away from the sun. (CSM Tracking)    -   5) Panels eventually return to the horizontal standby position.

The following several examples illustrate SM and CSM tracking and thetracking functions illustrated in FIGS. 23 through 28 and Table 1 assume90 degree AROM, sunrise at 6:00, sunset at 18:00 (equinox) and trackingconditions that allow 12 hours of continuous tracking Panel angles inTable 1 below are measured relative to the horizontal plane in eachexample. At the start of tracking, the time is 6:00, the sun angle is 0,and the panel angle is 0. The panel remains in the horizontal positionas the sun begins to rise.

Referring now to FIG. 23, the time is 7:00, the sun angle on the panelsis 15 degrees, the panel angle is 7 degrees, and the panels are turningslowly and simultaneously toward the sun (CSM tracking). Proper spacingprevents shadow cast onto the farthest panel from the sun. Referring nowto FIG. 24, the time is 8:00, the sun angle on the panels is 30 degrees,the panel angle is 16 degrees, the tracking process picks up speed asthe panels surfaces face the sun. Referring now to FIG. 25, the time is9:00, the sun angle on the panels is 45 degrees, and the panel angle isalso 45 degrees. The position is referred to as normal to the sun andthe position minimizes the AOI. At this point the panels stop and beginto reverse direction (SM tracking). Referring now to FIG. 26, the timeis 12:00, the sun angle on the panels is 90 degrees, and the angle ofthe panels is 0 representing the half way mark of the 12 hour trackingsequence. Referring now to FIG. 27, the time is 15:00, the sun angle onthe panels is 135 degrees, and angle of the panels is −45 degrees.

At this point the CSM returns with another reversal in direction ofmovement. The remainder of table 1 describes the return movement back toan idle horizontal position sampled at time 16:00, 17:00, and finally at18:00. The sampled angles of the sun on the panels is 150 degrees, 165degrees, and 180 degrees respectively. The panel angles on the sampledpoints are −16 degrees, −7 degrees, and 0 degrees where the panels havereturned to a horizontal position to wait for the next tracking sequenceat 6:00 the following day.

SUN PANEL TIME ANGLE ANGLE* EVENTS  6:00 0 0 As the sun starts ascent,the panel is in the horizontal starting position.  7:00 15 7 Panelsturning toward the sun (CSM) slowly to avoid shading. (FIG. 5)  8:00 3016 Panels pick up speed at it nears the encounter with the sun (FIG. 6) 9:00 45 45 When panel surfaces become 12:00 90 0 normal to the sun at9:00 (FIG. 7), 15:00 135 −45 they reverse direction and SM begins. Thehalf-way point is reached at 12:00 (FIG. 8). At 15:00 (FIG. 9), CSMreturns with another reversal. 16:00 150 −16 Panels are moving rapidlyaway from the sun to escape cross- shading. 17:00 165 −7 The speed hasslowed substantially as they near the “home” position. 18:00 180 0Panels are back in the horizontal position and ready for the next day.

Retrograde tracking using hybrid SM/CSM can be achieved with relativelysmall AROM and inter-panel/inter-array spacing compared to theconventional full-time SM tracking systems. These attributes areadvantageous wherever the tracking units have to be placed in arelatively close proximity of each other, especially for, but notlimited to rooftops. A method for tracking solar panels can becharacterized by beginning a tracking cycle substantially at sunrisewith adjacent tilting panels all horizontal; tilting the adjacent panelsin unison in a first angular direction toward the rising sun at a tiltrate that just avoids shading of adjacent panels; reversing direction ofpanel tilt at a point that the panels reach either a maximum tiltlimited by mechanical design, or the panel surfaces are orthogonal tothe rising sun; tilting the adjacent panels in a second angulardirection, following movement of the sun and keeping the surface of thepanels at right angles to the sun's position, until a point is reachedthat shadowing is imminent from the angle of the setting sun and thenreversing direction of panel tilt again to the first angular direction,adjusting tilt as the sun sets to avoid shading until the panels areagain horizontal. Small spacing requirement is also conducive forsmall-scale light-weight systems that can track at the device,panel/module level, in addition to larger array/cluster level. Thetracking system may minimize shading on adjacent panels in apre-programmed way such that the amount of shading is pre-known andcontrolled by varying the tilt angle and speed of tilt. In oneembodiment the shading varies according to the tilt angle.

One disadvantage of the retrograde tracking may be that the lower energygeneration efficiency of CSM tracking relative to SM tracking. However,the actual difference between full-time SM tracking and retrogradetracking should be relatively minor due to the fact that CSM portiontakes place during early-morning and late afternoon hours when the solarradiation is weak. The higher energy density of the retrograde trackingmethod may more than compensate for the slightly lower overallefficiency.

The ultimate choice of the tracking system may come down to theobjective of individual installations. If it is to simply maximizeenergy production (total watts/installation) with no space constraint, afull-time SM tracking system should be employed. However, if the goal isto attain the highest energy producing capacity for a given installationspace (watts/m2 or watts/ft2), retrograde tracking may be a betteroption. Development of a low-profile space-saving retrograde trackinghardware system may usher in a new era of rooftop-based tracking PVsystems in the future.

Modular Architecture

The inventor provides a unique low-profile modular architecture forrooftop and commercial solar panel arrays.

FIG. 28 is a perspective view illustrating two array configurationoptions according to an embodiment of the present invention. A solarpanel array 2800 comprises adjacent modular solar collection devices2802 installed in a linkable frame sub-system 2803. Devices 2802 arearrayed in a row and tilt along the length of the row in eitherdirection. Array 2800 includes adjustable frame legs 2804 for adjustingthe fixed angle of tilt to the slope of the roof. The individual solardevices or panels 2802 are linked to a tilting mechanism that providesSM and CSM tracking for all of the devices in unison.

A solar panel array 2801 comprises adjacent modular solar collectiondevices 2805 installed in a linkable frame sub-system 2806. Modulardevices 2805 are arrayed in adjacent columns, each 4 panels or devicesdeep the devices in each column tilting along the height of the columnin either direction.

FIG. 29 is a perspective view of a single sub-frame section of linkableframe component 2806 of FIG. 28. All of the modular devices are linkablethrough tilt mechanism to enable tracking in unison with each modulardevice of a linked sub-frame tilting in unison in the same direction.

FIG. 30 is a partial view of a frame member 3000 according to anembodiment of the present invention. Frame member 3000 includes aplurality of tilt mechanisms 3002 installed on a tilt-bar (one shown).Each tilt mechanism supports a single modular solar collection device. Atilt bar linking clip 3001 is provided in this example to enabletilt-bar linking through multiple adjacent-system frames. In this wayall of the modular devices in a device array can be linked to tilt inunison during SM and CSM tracking of the sun. A low-cost plain bearingis provided behind the linking clip to reduce tilt bar friction throughthe frame wall as it moves back and forth during tracking. The internalstructure 3003 of frame member 3000 is honeycombed to increase strengthwhile maintaining a light weight.

FIG. 31 is a perspective view of frame member 3000 of FIG. 30 showingouter skin and multiple tilt mechanisms. Frame member 3000 is a rightside frame member. A left side frame member would support the other sideof installed modular solar devices. Multiple tilt mechanisms 3002 arevisible on the inside wall of the frame. The outer skin covers theinternal honeycombed structure.

FIG. 32 is a block diagram illustrating basic tracking module componentsof a tracking module 3200. Tracking module 3200 is adapted to enable thesystem to perform both SM and CSM tracking as described previously. Onetracking module may control tracking for multiple linked solar devicearrays. Tracking module 3200 includes a rack and pinion 3201 installedon a linear guide. The rack slides on the linear guide and convertstorque into precision linear motion.

Module 3200 includes one or more magnetic limit sensors 3200. Sensors3200 enable calibration and validation of motor position in absence ofan encoder. Tracking module 3200 includes a power supply 3203 that isadapted to store electricity collected from the PV modules in capacitorsand for charging the battery. Tracking module 3200 includes a motor andreduction gear 3204 comprising a low cost and reliable stepper motor anda planetary gear head that is adapted to reduce speed and to boosttorque. Tracking module 3200 includes a logic/controller 3205 whichcomprises the brain of the system and communication center for thesystem.

The tracking module may in one embodiment include USB ports for enablingdiagnostic access to the device. The tracking module includes a batteryservice hatch for replacing rechargeable batteries, which may be a smallswap of small lithium batteries (about once every 3 years.)

FIG. 33 is a partial view of a frame member 3300 of the modular solarcollecting system of the present invention. Frame member 3300 has alow-set cross member. The frame sides that are parallel to PV panels arelowered and inside edges are rounded. This effectively increases thelevel of shade avoidance while tracking by the reduction in the minimumgap between the frame wall and first/last PV panel.

Frame member 3300 includes a push-on frame locking clip 3302 adapted torestrain movement between adjacent frames. In one embodiment, a bolt canbe inserted through the clip for reinforcement. Frame member 3200 hasoverlapping joints 3304 including adjacent walls that fit insidechannels and guides. The system also includes tight low-tolerance fitreinforced by studs. Outer coverings in the frame conceal a honeycombedinternal structure that provides reinforcing strength but remainsrelatively light weight.

It will be apparent to one with skill in the art that the modular solarsystem of the invention may be provided using some or all of thementioned features and components without departing from the spirit andscope of the present invention. It will also be apparent to the skilledartisan that the embodiments described above are specific examples of asingle broader invention which may have greater scope than any of thesingular descriptions taught. There may be many alterations made in thedescriptions without departing from the spirit and scope of the presentinvention.

1. A method for tracking solar panels comprising the steps of: (a)beginning a tracking cycle substantially at sunrise with adjacenttilting panels all horizontal; (b) tilting the adjacent panels in unisonin a first angular direction toward the rising sun at a tilt rate thatjust avoids shading of adjacent panels; (c) reversing direction of paneltilt at a point that the panels reach either a maximum tilt limited bymechanical design, or the panel surfaces are orthogonal to the risingsun; (d) tilting the adjacent panels in a second angular direction,following movement of the sun and keeping the surface of the panels atright angles to the sun's position, until a point is reached thatshadowing is imminent from the angle of the setting sun; (e) reversingdirection of panel tilt again to the first angular direction, adjustingtilt as the sun sets to avoid shading until the panels are againhorizontal.
 2. The method of claim 1 wherein, in steps (b) and (e) thetilting allows a pre-programmed constant percentage of shading to occur.3. The method of claim 1 wherein, in steps (b) and (e) the tiltingallows a pre-programmed percentage of shading to occur, and thepercentage varies with angle of tilt.
 4. The method of claim 1 whereintilting is accomplished in a continuous motion.
 5. The method of claim 1wherein tilting is accomplished incrementally at pre-programmed timeincrements
 6. A solar panel system comprising: a plurality of solarpanels having a length substantially greater than a width, mountedside-by-side with each panel enabled to tilt about along an axis in thedirection of the length of the panel; a tilting mechanism coupled toadjacent panels, capable of tilting the panels in either of two rotatingdirections about the panel axes; and a programmable drive controlenabled to control the rate and direction of tilt for the panels inunison in a tracking cycle; wherein the tracking cycle beginssubstantially at sunrise with the panels horizontal, the panels aretilted in unison in a first angular direction toward the rising sun at atilt rate that just avoids shading of adjacent panels, direction of tiltis reversed at a point that the panels reach either a maximum tiltlimited by mechanical design, or the panel surfaces are orthogonal tothe rising sun, the panels are tilted in a second angular direction,following movement of the sun and keeping the surface of the panels atright angles to the sun's position, until a point is reached thatshadowing is imminent from the angle of the setting sun, and tiltingdirection is reversed again to the first angular direction, adjustingtilt as the sun sets to avoid shading until the panels are againhorizontal.
 7. The system of claim 6 wherein the tilting allows apre-programmed constant percentage of shading to occur.
 8. The system ofclaim 6 wherein the tilting allows a pre-programmed percentage ofshading to occur and the percentage varies with angle of tilt.
 9. Thesystem of claim 6 wherein tilting is accomplished in a continuousmotion.
 10. The system of claim 6 wherein tilting is accomplishedincrementally at pre-programmed time increments.